Some heart defects in the conduction system result in asynchronous contraction (arrhythmia) of the heart and are sometimes referred to as conduction disorders. As a result, the heart does not pump enough blood, which may ultimately lead to heart failure. Conduction disorders can have a variety of causes, including age, heart (muscle) damage, medications and genetics.
Premature Ventricular Contractions (PVCs) are abnormal or aberrant heart beats that start somewhere in the heart ventricles rather than in the upper chambers of the heart as with normal sinus beats. PVCs typically result in a lower cardiac output as the ventricles contract before they have had a chance to completely fill with blood. PVCs may also trigger Ventricular Tachycardia (VT or V-Tach).
Ventricular tachycardia (VT or V-Tach) is another heart arrhythmia disorder caused by abnormal electrical signals in the heart ventricles. In VT, the abnormal electrical signals cause the heart to beat faster than normal, usually more than 100 beats per minute, with the beats starting in the heart ventricles. VT generally occurs in people with underlying heart abnormalities. VT can sometimes occur in structurally normal hearts, and in such patients the origin of abnormal electrical signals can be in multiple locations in the heart. One common location is in the right ventricular outflow tract (RVOT), which is the route the blood flows from the right ventricle to the lungs. In patients who have had a heart attack, scarring from the heart attack can create a milieu of intact heart muscle and a scar that predisposes patients to VT.
Other common causes for conduction disorders include defects in the left and/or right ventricle fast activation fibers, the His-Purkinje system, or scar tissue. As a result, the left and right ventricles may not be synchronized. This is referred to as Left Bundle Branch Block (LBBB) or Right Bundle Branch Block (RBBB).
Cardiac resynchronization therapy (CRT), also referred to as biventricular pacing or multisite ventricular pacing, is a known way to improve heart function in cases of LBBB or RBBB. CRT involves simultaneous pacing of the right ventricle (RV) and the left ventricle (LV) using a pacemaker. To implement CRT, a coronary sinus (CS) lead is placed for LV pacing in addition to a conventional RV endocardial lead (with or without a right atrial (RA) lead). The basic goal of CRT is to improve the mechanical functioning of the LV by restoring LV synchrony in patients with dilated cardiomyopathy and a widened QRS period, which is predominantly a result of LBBB.
Catheter ablation is a treatment of choice in patients with VT and/or symptomatic PVCs. The targets for ablation are locations in the heart where PVCs are occurring or locations where the onset of the VT is occurring. In order to determine a proper ablation location, a treating physician may first stimulate a proposed location using an electrical lead, in order to determine whether ablation at the proposed location will provide a desired electrical activation pattern stimulation of the heart.
Currently, determining the proper positioning of leads to obtain maximum cardiac synchronization or a desired electrical activation pattern involves a certain amount of guesswork on the part of an operating physician.
However, current methods do not allow for the determination of the optimal location for electrical leads, on a patient by patient basis. Further, if a desired activation pattern is not achieved when the heart is stimulated at a given location, current methods do not provide directional guidance for adjusting the lead location to provide an improved activation pattern. Accordingly, there is a need for improved guidance in determining the proper location for electrical leads for CRT and determining ablation locations.